LinkedList Simulate Number of Even Elements

An empty Linked List is given initially. Simulate the next operations:

- push front $x$: add element $x$ to the front of a Linked List; - push back $x$: add element $x$ to the back of a Linked List; - pop front: remove element from the front of a Linked List; - pop back: remove element from the back of a Linked List;

Let L = (a_1, a_2, \ldots, a_n) be the resulting Linked List. Find the number of all its even elements.

Nota

After simulation the list will have the next form:

The number of even elements is $1$.